Reef growth, southern Great Barrier Reef - preliminary results

The reefs of the Capricorn-Bunker Group in the southern Great Barrier Reef were the focus of a Bureau of Mineral Resources survey in September-October 1976. Subaerial and submarine exploration of seven reefs was conducted (Figure 1). The objectives of the expedition were: 1. To define the depth, shape and origin of the surface on which the present reefs rest. 2. To determine the effects of the present-day hydrologic regime on the growth of the reefs. 3. To define the time framework of modern growth. 4. To study the physical and chemical changes involved in the reef lithification processes. 5. To estimate the potential for metal accumulation of reef sediments and to determine the time of removal and deposition of metals in the carbonate sequence. The M. V. Escape was chartered from Gladstone to provide the platform for field studies. Shallow seismic refraction, echo profiling, underwater investigations using SCUBA, underwater coring, current, wave and water monitoring studies, and sediment sampling of lagoons were the principal field operations. Eighty-eight shallow seismic refraction traverses, each 120 m in length, were conducted using a Huntec FS-3 facsimile seismograph with a hammer or detonator sound source, and two subminiature land geophones or one pressure-sensitive hydrophone. The profiles cover windward and leeward algal ridges, cays, and in one case a lagoon and a lagoonal patch reef (One Tree Reef). This paper records field data and observations with the major emphasis placed on data relating to the morphologic growth of reefs. No attempt is made at this stage to present evidence relating to lithification or to processes and products of metal accumulation.